Add #[must_use] to From::from and Into::into
Risk of churn: **High**
Magic 8-Ball says: **Outlook not so good**
I figured I'd put this out there. If we don't do it now maybe we save it for a rainy day.
Parent issue: #89692
r? `@joshtriplett`
Speedup int log10 branchless
This is achieved with a branchless bit-twiddling implementation of the case x < 100_000, and using this as building block.
Benchmark on an Intel i7-8700K (Coffee Lake):
```
name old ns/iter new ns/iter diff ns/iter diff % speedup
num::int_log::u8_log10_predictable 165 169 4 2.42% x 0.98
num::int_log::u8_log10_random 438 423 -15 -3.42% x 1.04
num::int_log::u8_log10_random_small 438 423 -15 -3.42% x 1.04
num::int_log::u16_log10_predictable 633 417 -216 -34.12% x 1.52
num::int_log::u16_log10_random 908 471 -437 -48.13% x 1.93
num::int_log::u16_log10_random_small 945 471 -474 -50.16% x 2.01
num::int_log::u32_log10_predictable 1,496 1,340 -156 -10.43% x 1.12
num::int_log::u32_log10_random 1,076 873 -203 -18.87% x 1.23
num::int_log::u32_log10_random_small 1,145 874 -271 -23.67% x 1.31
num::int_log::u64_log10_predictable 4,005 3,171 -834 -20.82% x 1.26
num::int_log::u64_log10_random 1,247 1,021 -226 -18.12% x 1.22
num::int_log::u64_log10_random_small 1,265 921 -344 -27.19% x 1.37
num::int_log::u128_log10_predictable 39,667 39,579 -88 -0.22% x 1.00
num::int_log::u128_log10_random 6,456 6,696 240 3.72% x 0.96
num::int_log::u128_log10_random_small 4,108 3,903 -205 -4.99% x 1.05
```
Benchmark on an M1 Mac Mini:
```
name old ns/iter new ns/iter diff ns/iter diff % speedup
num::int_log::u8_log10_predictable 143 130 -13 -9.09% x 1.10
num::int_log::u8_log10_random 375 325 -50 -13.33% x 1.15
num::int_log::u8_log10_random_small 376 325 -51 -13.56% x 1.16
num::int_log::u16_log10_predictable 500 322 -178 -35.60% x 1.55
num::int_log::u16_log10_random 794 405 -389 -48.99% x 1.96
num::int_log::u16_log10_random_small 1,035 405 -630 -60.87% x 2.56
num::int_log::u32_log10_predictable 1,144 894 -250 -21.85% x 1.28
num::int_log::u32_log10_random 832 786 -46 -5.53% x 1.06
num::int_log::u32_log10_random_small 832 787 -45 -5.41% x 1.06
num::int_log::u64_log10_predictable 2,681 2,057 -624 -23.27% x 1.30
num::int_log::u64_log10_random 1,015 806 -209 -20.59% x 1.26
num::int_log::u64_log10_random_small 1,004 795 -209 -20.82% x 1.26
num::int_log::u128_log10_predictable 56,825 56,526 -299 -0.53% x 1.01
num::int_log::u128_log10_random 9,056 8,861 -195 -2.15% x 1.02
num::int_log::u128_log10_random_small 1,528 1,527 -1 -0.07% x 1.00
```
The 128 bit case remains ridiculously slow because llvm fails to optimize division by a constant 128-bit value to multiplications. This could be worked around but it seems preferable to fix this in llvm.
From u32 up, table lookup (like suggested [here](https://github.com/rust-lang/rust/issues/70887#issuecomment-881099813)) is still faster, but requires a hardware `leading_zeros` to be viable, and might clog up the cache.
Fix ICE when compiling nightly std/rustc on beta compiler
Fix#89775#89479 renames a lot of diagnostic items, but it happens that the beta compiler assumes that there must be DefId with `rustc_diagnostic_item = "send_trait"`, causing an ICE when compiling stage 0 std or stage 1 compiler. So gate it with `cfg(bootstrap)`.
The unwrap is also removed, so that existence of the diagnostic item is not required. I ripgreped the code base and this seems the only place where `unwrap` is called on the return value of `get_diagnostic_item`.
Add `Poll::ready` and revert stabilization of `task::ready!`
This PR adds an inherent `ready` method to `Poll` that can be used with the `?` operator as an alternative to the `task::ready!` macro:
```rust
let val = ready!(fut.poll(cx));
let val = fut.poll(cx).ready()?;
```
I think this form is a nice, non-breaking middle ground between changing the `impl Try for Poll`, and adding a separate macro. It looks better than `ready!` in my opinion, and it composes well:
```rust
let elem = ready!(fut.poll(cx)).pop().unwrap();
let elem = fut.poll(cx).ready()?.pop().unwrap();
```
The planned stabilization of `ready!` in 1.56 has been reverted because I think this alternate approach is worth considering.
r? rust-lang/libs
Add enum_intrinsics_non_enums lint
There is a clippy lint to prevent calling [`mem::discriminant`](https://doc.rust-lang.org/std/mem/fn.discriminant.html) with a non-enum type. I think the lint is worthy of being included in rustc, given that `discriminant::<T>()` where `T` is a non-enum has an unspecified return value, and there are no valid use cases where you'd actually want this.
I've also made the lint check [variant_count](https://doc.rust-lang.org/core/mem/fn.variant_count.html) (#73662).
closes#83899
Add #[must_use] to from_value conversions
I added two methods to the list myself. Clippy did not flag them because they take `mut` args, but neither modifies their argument.
```rust
core::str const unsafe fn from_utf8_unchecked_mut(v: &mut [u8]) -> &mut str;
std::ffi::CString unsafe fn from_raw(ptr: *mut c_char) -> CString;
```
I put a custom note on `from_raw`:
```rust
#[must_use = "call `drop(from_raw(ptr))` if you intend to drop the `CString`"]
pub unsafe fn from_raw(ptr: *mut c_char) -> CString {
```
Parent issue: #89692
r? ``@joshtriplett``
Add #[must_use] to alloc constructors
Added `#[must_use]`. to the various forms of `new`, `pin`, and `with_capacity` in the `alloc` crate. No extra explanations given as I couldn't think of anything useful to add.
I figure this deserves extra scrutiny compared to the other PRs I've done so far. In particular:
* The 4 `pin`/`pin_in` methods I touched. Are there legitimate use cases for pinning and not using the result? Pinning's a difficult concept I'm not very comfortable with.
* `Box`'s constructors. Do people ever create boxes just for the side effects... allocating or zeroing out memory?
Parent issue: #89692
r? ``@joshtriplett``
Cfg hide no_global_oom_handling and no_fp_fmt_parse
These are unstable sysroot customisation cfg options that only projects building their own sysroot will use (e.g. Rust-for-linux). Most users shouldn't care. `no_global_oom_handling` can be especially annoying since it's applied on many commonly used alloc crate methods (e.g. `Box::new`, `Vec::push`).
r? ```@GuillaumeGomez```
docs: `std:#️⃣:Hash` should ensure prefix-free data
Attempt to synthesize the discussion in #89429 into a suggestion regarding `Hash` implementations (not a hard requirement).
Closes#89429.
Improve docs for int_log
* Clarify rounding.
* Avoid "wrapping" wording.
* Omit wrong claim on 0 only being returned in error cases.
* Typo fix for one_less_than_next_power_of_two.
Add new tier-3 target: armv7-unknown-linux-uclibceabihf
This change adds a new tier-3 target: armv7-unknown-linux-uclibceabihf
This target is primarily used in embedded linux devices where system resources are slim and glibc is deemed too heavyweight. Cross compilation C toolchains are available [here](https://toolchains.bootlin.com/) or via [buildroot](https://buildroot.org).
The change is based largely on a previous PR #79380 with a few minor modifications. The author of that PR was unable to push the PR forward, and graciously allowed me to take it over.
Per the [target tier 3 policy](https://github.com/rust-lang/rfcs/blob/master/text/2803-target-tier-policy.md), I volunteer to be the "target maintainer".
This is my first PR to Rust itself, so I apologize if I've missed things!
Add documentation to boxed conversions
Among other changes, documents whether allocations are necessary
to complete the type conversion.
Part of #51430, supersedes #89199
Update to Unicode 14.0
The Unicode Standard [announced Version 14.0](https://home.unicode.org/announcing-the-unicode-standard-version-14-0/) on September 14, 2021, and this pull request updates the generated tables in `core` accordingly.
This did require a little prep-work in `unicode-table-generator`. First, #81358 had modified the generated file instead of the tool, so that change is now reflected in the tool as well. Next, I found that the "Alphabetic" property in version 14 was panicking when generating a bitset, "cannot pack 264 into 8 bits". We've been using the skiplist for that anyway, so I changed this to fail gracefully. Finally, I confirmed that the tool still created the exact same tables for 13 before moving to 14.
Add 'core::array::from_fn' and 'core::array::try_from_fn'
These auxiliary methods fill uninitialized arrays in a safe way and are particularly useful for elements that don't implement `Default`.
```rust
// Foo doesn't implement Default
struct Foo(usize);
let _array = core::array::from_fn::<_, _, 2>(|idx| Foo(idx));
```
Different from `FromIterator`, it is guaranteed that the array will be fully filled and no error regarding uninitialized state will be throw. In certain scenarios, however, the creation of an **element** can fail and that is why the `try_from_fn` function is also provided.
```rust
#[derive(Debug, PartialEq)]
enum SomeError {
Foo,
}
let array = core::array::try_from_fn(|i| Ok::<_, SomeError>(i));
assert_eq!(array, Ok([0, 1, 2, 3, 4]));
let another_array = core::array::try_from_fn(|_| Err(SomeError::Foo));
assert_eq!(another_array, Err(SomeError::Foo));
```
Add #[must_use] to string/char transformation methods
These methods could be misconstrued as modifying their arguments instead of returning new values.
Where possible I made the note recommend a method that does mutate in place.
Parent issue: #89692
Fix minor std::thread documentation typo
callers of spawn_unchecked() need to make sure that the thread
not outlive references in the passed closure, not the other way around.
